Diagnostics on an atmospheric pressure plasma jet

The atmospheric pressure plasma jet (APPJ) is a homogeneous non-equilibrium discharge at ambient pressure. It operates with a noble base gas and a percentage-volume admixture of a molecular gas. Applications of the discharge are mainly based on reactive species in the effluent. The effluent region of a discharge operated in helium with an oxygen admixture has been investigated. The optical emission from atomic oxygen decreases with distance from the discharge but can still be observed several centimetres in the effluent. Ground state atomic oxygen, measured using absolutely calibrated two-photon laser induced fluorescence spectroscopy, shows a similar behaviour. Detailed understanding of energy transport mechanisms requires investigations of the discharge volume and the effluent region. An atmospheric pressure plasma jet has been designed providing excellent diagnostics access and a simple geometry ideally suited for modelling and simulation. Laser spectroscopy and optical emission spectroscopy can be applied in the discharge volume and the effluent region.

Electronic excitation in metals through hyperthermal atoms

A hyperthermal hydrogen/deuterium atom beam source with a defined energy distribution has been employed to investigate the kinetically induced electron emission from noble metal surfaces. A monotonous increase in the emission yield was found for energies between 15 and 200 eV. This, along with an observed isotope effect, is described in terms of a model based on Boltzmann type electron energy distributions.

Determination of quenching coefficients in a hydrogen RF discharge by time-resolved optical emission spectroscopy

In gas discharges at elevated pressure, radiation-less collisional de-excitation (quenching) has a strong influence on the population of excited states. The knowledge of quenching coefficients is therefore important for plasma diagnostics and simulations. A novel time-resolved optical emission spectroscopic (OES) technique allows the measurement of quenching coefficients for emission lines of various species, particularly of noble gases, with molecular hydrogen as collision partner. The technique exploits the short electron impact excitation during the field reversal phase within the sheath region of a hydrogen capacitively coupled RF discharge at 13.56 MHz. Quenching coefficients can be determined subsequent to this excitation from the effective lifetime of the fluorescence decay at various hydrogen pressures. The measured quenching coefficients agree very well with results obtained by means of laser excitation. The time-resolved OES technique based on electron impact excitation is not limited - in contrast to laser techniques - by optical selection rules and the energy gap between the ground state and the observed excited level.

Substrate evaluation for a microbeam endstation using unstained cell imaging.

A cellular imaging system, optimized for unstained cells seeded onto a thin substrate, is under development. This system will be a component of the endstation for the microbeam cell-irradiation facility at the University of Surrey. Previous irradiation experiments at the Gray Cancer Institute (GCI) have used Mylar film to support the cells [Folkard, M., Prise, K., Schettino, G., Shao, C., Gilchrist, S., Vojnovic, B., 2005. New insights into the cellular response to radiation using microbeams. Nucl. Instrum. Methods B 231, 189-194]. Although suitable for fluorescence microscopy, the Mylar often creates excessive optical noise when used with non-fluorescent microscopy. A variety of substrates are being investigated to provide appropriate optical clarity, cell adhesion, and radiation attenuation. This paper reports on our investigations to date.

Absolute Calibration of Atomic Density Measurements by Laser-Induced Fluorescence Spectroscopy with Two-Photon Excitation (TALIF)

The two-photon resonances of atomic hydrogen (? = 2 × 205.1 nm), atomic nitrogen (? = 2 × 206.6 nm) and atomic oxygen (? = 2 × 225.6 nm) are investigated together with two selected transitions in krypton (? = 2×204.2 nm) and xenon (? = 2×225.5 nm). The natural lifetimes of the excited states, quenching coefficients for the most important collisions partners, and the relevant ratios of the two-photon excitation cross sections are measured. These data can be applied to provide a calibration for two-photon laser-induced fluorescence measurements based on comparisons with spectrally neighbouring noble gas resonances.

Absolute Atomic Oxygen Density Distributions in the Effluent of a Micro Scale Atmospheric Pressure Plasma Jet

The coplanar microscale atmospheric pressure plasma jet (µ-APPJ) is a capacitively coupled radio frequency discharge (13.56 MHz, ~15W rf power) designed for optimized optical diagnostic access. It is operated in a homogeneous glow mode with a noble gas flow (1.4 slm He) containing a small admixture of molecular oxygen (~0.5%). Ground state atomic oxygen densities in the effluent up to 2 × 1014 cm-3 are measured by two-photon absorption laser-induced fluorescence spectroscopy (TALIF) providing space resolved density maps. The quantitative calibration of the TALIF setup is performed by comparative measurements with xenon. A maximum of the atomic oxygen density is observed for 0.6% molecular oxygen admixture. Furthermore, an increase in the rf power up to about 15W (depending on gas flow and mixture) leads to an increase in the effluent’s atomic oxygen density, then reaching a constant level for higher powers.

Measurement of Quenching Coefficients and Developement of Calibration Methods for Quantitative Spectroscopy of Plasma at Elevated Pressures

Measurements of collisional de-excitation (quenching) coefficients required for the interpretation of emission and fluorescence spectroscopic measurements are reported. Particular attention is turned on argon transitions which are of interest for actinometric determinations of atomic ground state populations and on fluorescence lines originating from excited atoms and noble gases in connection with two-photon excitation (TALIF) of atomic radicals. A novel method is described which allows to infer quenching coefficients for collisions with molecular hydrogen of noble gas states in the energy range up to 24 eV. The excitation is performed in these experiments by collisions of energetic electrons in the sheath of an RF excited hydrogen plasma during the field reversal phase which lasts about 10 ns. We describe in addition a calibration method - including quenching effects - for the determination by TALIF of absolute atomic radical densities of hydrogen, nitrogen and oxygen using two-photon resonances in noble gases close by the resonances of the species mentioned. The paper closes with first ideas on a novel technique to bypass quenching effects in TALIF by introducing an additional, controllable loss by photoionization that will allow quenching-free determination of absolute atomic densities with prevalent nanosecond laser systems in situations where collisional de-excitation dominates over spontaneous emission.

FARM_2DRMP: A version of FARM for use with 2DRMP

To complete the 2DRMP package an asymptotic program, such as FARM, is needed. The original version of FARM is designed to construct the physical R-matrix, R, from surface amplitudes contained in the H-file. However, in 2DRMP, R has already been constructed for each scattering energy during propagation. Therefore, this modified version of FARM, known as as FARM_2DRMP, has been developed solely for use with 2DRMP.

HBrowse: a GRACE tool for browsing R-matrix H-files

An H-file is used to convey information from the inner-region to the outer-region in R-matrix computations. HBrowse is a workstation tool for displaying a graphical abstraction of a local or remote R-matrix H-file. While it is published as a stand-alone tool for post-processing the output from R-matrix inner-region computations it also forms part of the Graphical R-matrix Atomic Collision Environment (GRACE), HBrowse is written in C and OSF/Motif for the UNIX operating system. (C) 2000 Elsevier Science B.V. All rights reserved.

Dramatic solvent effects on ring-opening metathesis polymerization of cycloalkenes

A series of metathesis polymers and copolymers have been formed and their structures were analysed by C-13 NMR spectroscopy. Noble metal and non-noble metal salt catalysts are distinguished by their behaviour in various solvents. Thus, in phenolic solvents, the former class produce alternating copolymers from cyclopentene and norbornene, while the latter are unaffected and produce random copolymers. In contrast, ether solvents have the effect of markedly increasing the cis content of polymers from the latter catalysts while the former are unaffected.